This application is based on Japanese Patent Applications No. 2001-223764 filed on Jul. 25, 2001, No. 2001-226914 filed on Jul. 27, 2001, No. 2001-241509 filed on Aug. 9, 2001, No. 2001-249345 filed on Aug. 20, 2001, and No. 2001-266638 filed on Sep. 4, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a leak-check apparatus of a fuel-vapor-processing system, a fuel-temperature estimation apparatus and a fuel-temperature-sensor diagnosis apparatus.
2. Description of Related Art
U.S. Pat. No. 6,082,337 (JP-A-11-101162) discloses an apparatus, which is used for checking a leak on a passage of a fuel-vapor-processing system during a running state of the engine. In a running state of the engine, however, the level of fuel in a fuel tank varies. It is thus difficult to check a leak with a high degree of precision during a running state of the engine.
On the other hand, JP-A-6-81727 (Japan Patent No. 2,745,991) discloses leak-check processing, which is carried out after the engine is stopped. However, leak-check processing, which is carried out after the engine is stopped, exhausts the battery.
U.S. Pat. No. 5,263,462 discloses an apparatus, which is used for detecting a pressure in the passage when the temperature of the fuel tank increases by a predetermined quantity, and used for checking a leak of the same system on the basis of this pressure. When the ambient temperature is low, however, the temperature of fuel in the fuel tank may not increase. Thus, the number of times the leak-check processing is carried out decreases.
In the leak-check processing, a leak is checked by hermetically sealing the passage of the system. Thus, when the passage of the system is opened after the leak-check processing, a flow is generated in the system due to a difference in pressure between the system and the atmosphere. If a flow is generated in a canister, for example, fuel vapor transits to an undesirable state in some cases.
In leak-check processing, detection of a small leak is also demanded. In the case of a small leak, however, it takes a long time to generate a detectable change in pressure. Thus, in order to detect a small leak, a long check time is required. During such a long check time, however, it is quite within the bounds of possibility that the operating condition of the engine changes. It is thus difficult to detect a small leak.
JP-A-6-81727 discloses a leak-check apparatus provided with a sensor for detecting a temperature of fuel in the fuel tank. This apparatus finds a difference in fuel temperature between a stopped state of the engine and a start of the engine. If the difference in fuel temperature is found greater than a predetermined value, a leak is checked on the basis of an internal pressure of the fuel tank. However, the fuel-temperature sensor increases the number of components and brings about an increase in assembly man-hour.
It is thus an object of the present invention to provide an improved fuel-vapor-processing system capable of solving the problems raised by the conventional technology.
It is another object of the present invention to provide a leak-check apparatus capable of detecting a leak in a fuel-vapor-processing system with a high degree of precision and reducing the amount of consumed power generated by the battery in a stopped state of the engine.
It is a further object of the present invention to provide the fuel-vapor-processing system with a leak-check apparatus capable of carrying out leak-check processing at a proper frequency.
It is a still further object of the present invention to provide the fuel-vapor-processing system with a leak-check apparatus capable of making it difficult for air to flow into the system after leak-check processing.
It is a still further object of the present invention to provide the fuel-vapor-processing system with a leak-check apparatus capable of executing a leak-check procedure over a long period of time.
It is a still further object of the present invention to provide a fuel-temperature estimation apparatus for estimating a temperature of fuel in the fuel tank.
It is a still further object of the present invention to provide the fuel-vapor-processing system with a leak-check apparatus for estimating a temperature of fuel in the fuel tank and checking a leak in the fuel-vapor-processing system on the basis of the estimated temperature of the fuel.
It is a still further object of the present invention to provide a diagnosis apparatus for diagnosing a fuel-temperature sensor for detecting a temperature of fuel in the fuel tank.
According to a first aspect of the present invention, only if a preliminary leak is determined to exist in the fuel-vapor-processing system by an engine-running-state leak-check function of an engine-running-state leak-check means, is an engine-stopped-state leak-check function of an engine-stopped-state leak-check means executed so that a leak in a fuel-vapor-processing system can be detected and the power consumption in a stopped state of the engine can be reduced.
A small leak detected by the engine-running-state leak-check means may be regarded as a preliminary leak in the fuel-vapor-processing system and, when the engine-running-state leak-check means detects a preliminary leaks, the engine-stopped-state leak-check means may then confirm the leak.
It is also possible to provide a configuration wherein, when the engine-stopped-state leak-check means detects a leak in the fuel-vapor-processing system, only the engine-running-state leak-check means determines whether a normal condition has been restored in the fuel-vapor-processing system.
Thus, once a leak has been determined to exist in the fuel-vapor-processing system, only the engine-running-state leak-check means carries out leak-check processing in the fuel-vapor-processing system so that it is possible to reduce the amount of power consumed by an ECU in a stopped state of the engine.
According to a second aspect of the present invention, in the above configuration, a pressure in the fuel-vapor-processing system is detected within a leak-check period following termination of the running state of the engine and leak-check processing is carried out on the basis of the detected pressure. Thus, even if the temperature of fuel in the fuel tank increases only slightly after the running state of the engine is stopped, a condition for execution of the leak-check processing becomes easier to satisfy. As a result, leak-check processing can be carried out if necessary after the running state of the engine is stopped so that the frequency of the leak-check processing can be increased.
According to a third aspect of the present invention, the pressure of the fuel-vapor-processing system is limited to values lower than a predetermined limit during a leak-check period. Thus, when an open-air opening/closing valve of the canister is opened to expose the fuel-vapor-processing system to the atmosphere after the leak-check processing is finished, gas can be prevented from forcibly flowing into the canister and the fuel component in the canister can thus be prevented from being blown to the atmosphere.
According to a fourth aspect of the present invention, when the running state of the engine is stopped in the course of leak-check processing, a leak-check means continues an operation to supply power to components required for continuing the leak-check processing so that the leak-check processing can be carried out to its end. By doing so, even if there are more chances that the running state of the engine is stopped in the course of leak-check processing due to the fact that a long leak-check period is required for detecting a small leak, the leak-check processing is continued even after the running state of the engine is stopped so that it is possible to determine whether a leak exists in the fuel-vapor-processing system. Thus, the number of times the leak-check processing is carried out can be increased. As a result, detection of a small leak and early detection of a leak can be accomplished at the same time.
According to a fifth aspect of the present invention, there is provided a fuel-temperature estimation apparatus comprising:
a fuel-temperature-increase estimation means for estimating an increase in fuel temperature in the fuel tank in a running state of the engine on the basis of a state of the operation;
a fuel-temperature-decrease estimation means for estimating a decrease in fuel temperature in the fuel tank on the basis of a vehicle speed and/or an intake-air temperature as well as information (such as an ambient-air temperature) having correlation with the vehicle speed and the intake-air temperature wherein the decrease is caused by a cooling effect (or an outgoing-radiation effect); and
a fuel-temperature estimation means for updating the present estimated value of the fuel temperature on the basis of a fuel-temperature increase estimated by the fuel-temperature-increase estimation means and a fuel-temperature decrease estimated by the fuel-temperature-decrease estimation means.
In this configuration, it is thus possible to determine a temperature of fuel in the fuel tank in a running state of the engine without the need to provide a fuel-temperature sensor.
The fuel-temperature-increase estimation means may estimate an increase in fuel temperature in the fuel tank wherein the increase is caused by radiated heat propagating into the fuel tank. As an alternative, the fuel-temperature-increase estimation means may estimate an increase in fuel temperature in the fuel tank on the basis of a signal output by an exhaust-temperature sensor. As another alternative, the fuel-temperature-increase estimation means may estimate an increase in fuel temperature in the fuel tank on the basis of the engine""s revolution speed and/or load including an intake-pipe pressure, an intake air volume and a throttle opening. In general, the amount of exhaust-gas heat increases in proportion to the engine""s revolution speed and load. Thus, a fuel-temperature increase caused by exhaust-gas heat can be estimated on the basis of the engine""s revolution speed and load.
A so-called increase in fuel temperature in a fuel return system is caused by return fuel in addition to exhaust-gas heat. The return fuel is fuel returned from a fuel injection valve to the fuel tank. An increase in fuel temperature in the fuel return system may also be estimated by considering these 2 major causes, namely, the exhaust-gas heat and the return fuel. In this way, an increase in fuel temperature can be estimated with a high degree of precision. It is to be noted that, in a fuel return system where no fuel is returned from the fuel injection valve to the fuel tank, an increase in fuel temperature can thus be estimated by considering only an effect of the exhaust-gas heat, without the need to take a fuel-temperature increase caused by return fuel into account.
As a further alternative, a fuel-temperature increase caused by heat generated by a fuel pump may also be estimated. In this case, the amount of heat generated by the fuel pump can be estimated from power supplied to the fuel pump.
Even if the amounts of heat received and radiated by fuel in the fuel tank are equal to each other, a fuel-temperature change may vary in dependence on the amount of residual heat in the fuel tank. For example, the fuel-temperature increase caused by, among others, exhaust-gas heat tends to rise for a small amount of residual heat in the fuel tank. In addition, for a high temperature of fuel in the fuel tank, the difference in temperature between the running resistance wind (or outside air) and the fuel is big. In this case, the fuel-temperature decrease caused by a cooling effect (or an outgoing-radiation effect) tends to increase. For a low temperature of fuel in the fuel tank, on the other hand, the fuel-temperature increase caused by, among others, exhaust-gas heat tends to rise relatively. The present estimated value of the fuel temperature can be corrected by a correction means on the basis of the amount of fuel left in the fuel tank and/or the previous estimated value of the fuel temperature. In this way, the temperature of fuel can be estimated with a higher degree of precision.
A fuel-temperature decrease caused by dissipated heat during a stopped state of the engine is estimated on the basis of the lapse of time since a previous stopped state of the engine till the present start of the engine and an ambient temperature or information having a correlation with the ambient temperature. An example of such information is an intake-air temperature. Then, an initial value of the fuel temperature at the present start of the engine can be estimated by subtracting the fuel-temperature decrease caused by dissipated heat during the stopped state of the engine from the fuel temperature""s estimated value estimated for the previous stopped state of the engine. If the fuel temperature""s initial value estimated in this way is lower than the ambient temperature (or the intake-air temperature), the initial value of the fuel temperature can be set at the ambient temperature (or the intake-air temperature).
The fuel temperature""s value estimated in a stopped state of the engine may be updated on the basis of the lapse of time since the termination of the engine operation or information having a correlation with the lapse of time. An example of such information is a decrease in cooling-water temperature after the termination of the engine operation. The fuel temperature""s value estimated in a stopped state of the engine may be updated on the basis of the lapse of time since the termination of the engine operation and the ambient temperature or information having a correlation with the lapse of time and the ambient temperature. The present estimated value of the fuel temperature may be corrected on the basis of the amount of fuel left in the fuel tank.
It is possible to provide a configuration comprising a fuel-temperature estimation apparatus for estimating a temperature of fuel in the fuel tank during a running state of the engine and a fuel-temperature estimation apparatus for estimating a temperature of fuel in the fuel tank in a stopped state of the engine. The former and the latter apparatus are referred to hereafter as an engine-running-state fuel-temperature estimation apparatus and an engine-stopped-state fuel-temperature estimation apparatus respectively. With such a configuration, a temperature of fuel can be estimated during both a running state of the engine and a stopped state of the engine.
According to a sixth aspect of the present invention, an estimated value of the fuel temperature is used as a leak-check execution condition criterion parameter and/or a leak-check parameter. Without providing a fuel-temperature sensor, a leak in the fuel-vapor-processing system can thus be checked by consideration of the fuel tank""s fuel temperature estimated during a running state of the engine or in a stopped state of the engine.
In this case, a leak in the fuel-vapor-processing system can be checked on the basis of a relation between the change in fuel-temperature value estimated in a stopped state of the engine and the change in fuel-tank internal pressure in the stopped state. In a stopped state of the engine, the temperature of fuel in the fuel tank gradually decreases with the lapse of time due to dissipation of heat. In the stopped state, evaporation gas in the spatial portion of the fuel tank condenses gradually, causing the amount of the evaporation gas to gradually decrease as well. Thus, if the fuel-vapor-processing system including the fuel tank is hermetically sealed, the internal pressure of the fuel tank gradually goes down with the lapse of time, indicating that the fuel-vapor-processing system is in a normal state with no leak. If there is a leak in the fuel-vapor-processing system, on the other hand, the internal pressure of the fuel tank does not change, remaining at a value close to the atmospheric pressure even if the temperature of fuel in the fuel tank decreases. For this reason, a leak in the fuel-vapor-processing system can be checked on the basis of a relation between the change in fuel-temperature value estimated in a stopped state of the engine and the change in fuel-tank internal pressure in the stopped state.
For example, a leak in the fuel-vapor-processing system may be checked on the basis of a change in fuel-tank internal pressure during a period, which starts when the check-leak processing is commenced in a stopped state of the engine and ends when the fuel temperature""s value estimated in the stopped state decreases to a predetermined value. That is, a leak or no leak is determined to exist in the fuel-vapor-processing system if the internal pressure of the fuel tank decreases only by a quantity smaller or greater respectively than a criterion value when the fuel temperature""s value estimated in the stopped state of the engine decreases to the predetermined value.
It is to be noted that a leak in the fuel-vapor-processing system may also be checked on the basis of a decreasing gradient of the estimated value in a predetermined period of time and a variation gradient of the internal pressure in the same predetermined period of time, wherein the decreasing gradient is defined as a rate of decrease in fuel-temperature estimated value whereas the variation gradient is defined as a rate of change in fuel-tank internal pressure.
If the temperature of fuel in the fuel tank is low at the start of processing to check a leak in the fuel-vapor-processing system in a stopped state of the engine, that is, if the temperature of fuel in the fuel tank is close to the ambient temperature, the temperature of fuel decreases thereafter only by a small quantity. Thus, the change in fuel-tank-internal-pressure also becomes smaller as well so that the difference in internal-pressure change between a leaked state and the normal state is small. As a result, it is difficult to distinguish a leaked state and the normal state from each other.
In order to solve this problem, a condition requiring the fuel temperature""s value estimated immediately before or immediately after termination of the engine operation to be higher than the ambient temperature by at least a predetermined difference may be set as one of conditions for execution of the leak-check processing. By setting such a condition as a condition for execution of the leak-check processing, it is possible to assure a sufficient decrease in fuel temperature (or a sufficient rate of decrease in fuel temperature) during the leak-check processing carried out in a stopped state of the engine. Thus, it is possible to clearly distinguish a change in fuel-tank-internal-pressure (or a rate of change in fuel-tank-internal-pressure) in a leaked state from a change in fuel-tank-internal-pressure (or a rate of change in fuel-tank-internal-pressure) in a normal state. As a result, it is possible to determine whether a leak exists in the fuel-vapor-processing system with a high degree of precision.
According to a seventh aspect of the present invention, a fuel-temperature sensor is diagnosed for existence/non-existence of an abnormality on the basis of a relation between an estimated value of the fuel temperature and a temperature value detected by the fuel-temperature sensor. If the difference between an estimated value of the fuel temperature and a temperature value detected by the fuel-temperature sensor is beyond a range of the normal state, for example, the result of the diagnosis of the fuel-temperature can be set to indicate that the sensor is abnormal. As an alternative, the fuel-temperature sensor is diagnosed for existence/non-existence of an abnormality on the basis of a relation between a change in fuel-temperature estimated value and a change in fuel-temperature-sensor detected value. This is because the estimated value of the fuel temperature varies in dependence on how an initial value of the estimated fuel temperature is set. By using the change in fuel-temperature estimated value in place of the estimated value of the fuel temperature, this problem can be solved. This is because the change in fuel-temperature estimated value is all but independent of how an initial value of the estimated fuel temperature is set. Thus, by diagnosing the fuel-temperature sensor for existence/non-existence of an abnormality on the basis of a relation between a change in fuel-temperature estimated value and a change in fuel-temperature-sensor detected value, the fuel-temperature sensor can be diagnosed for existence/non-existence of an abnormality with a high degree of precision even if the initial value of the estimated fuel temperature changes more or less.